Thermochemical sulfate reduction a review |
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Authors: | T P Goldstein Z Aizenshtat |
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Institution: | (1) Central Research Laboratory, Mobil Research and Development Corp., P.O.Box 1025, 08543 Princeton, N.J., USA;(2) Energy Research Center, Casali Institute For Applied Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel |
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Abstract: | The high concentrations of hydrogen sulfide found in many oil and gas fields is thought to arise from the oxidation of petroleum
hydrocarbons by sulfate—a reaction that reduces the value of the resource. This review, undertaken in order to better understand
the geochemistry of TSR reaction in oil field sediments, covers the relevant information on thermochemical sulfate reduction
(TSR) to 1991. The theoretical and experimental aspects of TSR reactions (including sulfur and carbon isotope studies) are
reviewed and their significance to the geochemical system discussed. The present review agrees with previous suggestions that
biochemical reduction of sulfate dominates in sedimentary environments below 120°C, and supports the possibility that reactive
sulfur species will oxidize certain organic molecules at meaningful rates in geochemically reasonable reaction periods at
temperatures above 175°C. We conclude that under typical petroleum reservoir reaction conditions, both elemental sulfur and
polysulfides are capable of oxidizing some organic molecules under basic conditions. But that sulfate alone will not react
unless lower oxidation state sulfur is present. The possible interaction of low-valence-state sulfur with sulfate to form
TSR active oxidants is examined. both H2S and SO
4
2−
are required for the formation of active polysufide reductants (e.g. thiosulfate or polythionates) in TSR systems. Such intermediates
can serve to lower the overall activation energy of the oxidation of hydrocarbons by sulfate via thermal generation of sulfur
radicals that can function as TSR active oxidants in many oil field sediments. We suggest that some proposed chemical mechanisms
for TSR need to be experimentally verified and the results re-interpreted with respect to TSR relations in geologic systems.
Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65th birthday |
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Keywords: | thermochemical sulfate reduction (TSR) |
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